The power supplies in a computer system are designed to meet the specific power requirements of the integrated circuit chips (ICs) that are the components of the system. The nominal operating voltages for the ICs are typically known because most ICs are manufactured to meet industry standards for device operation. For example, the nominal supply voltage for transistor-transistor logic (TTL) devices is 5.0 volts while the nominal supply voltage for complementary metal oxide semiconductor (CMOS) devices is 3.3 volts.
A power supply ideally delivers the nominal voltage levels with assurance and precision, but power supplies are typically inaccurate due to a number of factors. A typical range of assurance for a power supply is plus or minus five percent. Accordingly, most ICs are designed to operate within a range of plus or minus five percent of the nominal voltage. However, some ICs are less tolerant to power supply inaccuracies, and some ICs may require a nominal operating voltage other than the standard TTL and CMOS voltages. The operating voltage of an IC having either one or both of these characteristics can be supplied by DC-DC converter that converts the DC output of the power supply into the desired DC operating voltage.
DC-DC converters are typically switching voltage regulators, which are more efficient than linear regulators. The need for efficiency is emphasized when the DC-DC converter is to be used to supply voltage to a single IC, which could be the processor of the computer system. If too much power is dissipated while the DC-DC converter is operating, heat sinks will be needed and the footprint of the DC-DC converter will be increased. This is especially undesirable when the amount of available board space is limited.
Furthermore, maximum current consumption, current density and current transient demands of high performance microprocessors have been increasing by 50% per generation in spite of supply voltage (VCC) scaling. Reduction of VCC makes the problem of delivering larger currents with high conversion efficiency even more challenging, especially since the maximum acceptable VCC variation is on the order of 10% of the target VCC value. Employing traditional methods to meet VCC variation targets on the microprocessor die in the presence of large current transients requires a prohibitively large amount of on-die decoupling capacitance (decap). Alternately, a motherboard voltage regulator and converter module (VRM) is required to operate at a higher frequency.